Storage Characteristics

Storage devices can be described by their physical storage characteristics. These characteristics include whether or not the device can store data permanently; how the computer system locates data in the device; and whether or not it needs constant electric power to store data.

Permanent and non-permanent

Permanent means 'protected against any alterations'. No data storage device will last forever, but it is possible to protect it against data changes during its life. A device is non-permanent if it can be altered.

Random and sequential

Sequential access means that the storage locations have to be read or written in their correct order, starting with the first location. For example, if you need to restore just one file from a tape backup the only way you (or the backup software) can find the file is to start at the beginning of the tape and search it byte by byte.
Sequential access is the slowest. This speed problem means that it is used almost entirely for long-term data storage and for data backups.
Random access means that any storage location can be directly read or written. Random access is also called 'direct access'. It is much faster and more efficient than sequential access devices. If the starting address or location of the file is known then you can move directly to it. Random access relies on knowing the exact position of the stored data.

Volatile and non-volatile

Volatile refers to storage devices that will lose all their data if the power is switched off. Less common. RAM is the only storage device that needs constant power supply to keep its data, making it volatile.
Volatility is a term used in information processing. It refers to the percentage of records that are added to or deleted from a file during a single processing operation. A data file that has a high percentage of changes would be described as having a high volatility.

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